Reduce strong mode errors and warnings

pkg/front_end/lib/src/fasta/builder/member_builder.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library fasta.member_builder;
 
 import 'builder.dart' show
     Builder,
     ClassBuilder,
     ModifierBuilder;
 
+import 'package:meta/meta.dart' show
+    virtual;
+
 abstract class MemberBuilder extends ModifierBuilder {
-  Builder parent;
+  // TODO(sigmund): remove @virtual, should not be needed, see #28601
+  @virtual Builder parent;
+
+  String get name;

[Siggi Cherem (dart-lang), 2017/02/02 04:26:58]

I wasn't sure about adding it here, but there wasn't any common superclass of
Field and Procedure that could have this (there is one place where you read
member.name to provide an error message)

 
   bool get isInstanceMember => isClassMember && !isStatic;
 
   bool get isClassMember => parent is ClassBuilder;
 
   bool get isTopLevel => !isClassMember;
 }